Hi Vikram,
I ran the patch set on my x86-box to get familiar with the WALT internals. Unfortunately I'm not part of the EAS product initiative so this is my first encounter with it. However, my humble knowledge of PELT might help creating a WALT patch-set LKML folk might appreciate.
Cheers,
-- Dietmar
On 03/09/16 00:27, markivx@codeaurora.org wrote:
This patch series implements an alternative window assisted load tracking mechanism in lieu of PELT based cpu utilization tracking. Testing has shown that a window based non-decaying metric such as WALT guiding cpu frequency and task placement decisions can improve performance/power especially when running workloads more commonly found on mobile devices. The aim of this series is to incorporate WALT accounting into the scheduler and feed WALT statistics to schedutil in order to guide cpu frequency selection. The implementation is detailed in the commit text of Patch 1. The eventual goal is to also guide placement decisions based on WALT statistics.
By placement you mean EAS/capacity aware wakeup or does it include load-balance?
WALT has existed in out-of-tree kernels for ARM/ARM64 commercialized devices for a few years. This is an effort to bring WALT to mainline as well as to test on multiple architectures and with varied workloads.
This RFC version is mainly to preview what the code will look like on mainline. Future RFC revisions will include a theoretical discussion and benchmark results.
This would be the more interesting part (the 'why' (TM Morten R.) we would have to replace PELT util with WALT. And this also in perspective to the recent effort from Vincent G. to fix util for task groups on LKML.
Tested on an Intel x86_64 machine (on top of 4.7-rc6). (Benchmark results will be sent out separately and as part of this message in the next RFC version).
Run 'perf bench sched messaging -g 20 -l 5000' on my 'Intel Core i7-4750HQ CPU @ 2.00GHz' on v4.7 and v4.7+ and didn't see much difference. So we probably need some more clever workloads to evaluate the overhead of this extra locking.
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